1. Field of the Invention
The present invention relates to a head-rest device for a vehicle seat or the like and, more particularly, to an improved head-rest device which can be adjusted vertically relative to a seat back.
2. Description of the Prior Art
A head-rest device of this type must be capable of vertical adjustments of its height so that it can be applied to many occupants of varying sitting heights. Since this vertical height adjustment is to be made manually, it is preferred that such head-rest device can be operated with a light force to adjust its height. With such light-force design, however, when heavy shocks are given, the head-rest device will be unnecessarily lowered in height. For example, when shocks are applied to the head of an occupant in case of a rear-end collision or the like, a force acting in a direction to push down the head-rest device is produced; since this kind of push-down force is usually considerably large, the head-rest device of such light-force design will be forced to go down unnecessarily and sharply, and thus it fails to safely hold the occupant. This means it is difficult to simultaneously satisfy both requirements of easy manual operation and safety holding.
Therefore, in order to satisfy these two conflicting needs at the same time, that is, an easy height adjustment and a positive holding of a predetermined position against shocks applied from above, there have been conventionally proposed and practiced various kinds of head-rest devices which are provided with a lock mechanism between head-rest stays and their associated head-rest holders.
However, these conventional head-rest devices are complicated in structure. Thus, most of them include a stepwise adjustment lock mechanism in which each of the head-rest stays is formed with some cutaway portion in which an engagement member on the side of the associated head-rest holder is pressed against and engaged with the cutaway portion of the head-rest stay so as to hold the head-rest stay vertically. With such stepwise adjustment lock mechanism, a fine positional adjustment of the head-rest stay is impossible and thus it is not possible to set the height of the head-rest to its best position with respect to various occupants. Also, the formation of the cutaway portion in the heat-rest stay presents a problem since it decreases the strength of the head-rest stay and thus that of the entire head-rest device.